Research On Direct Torque Control For Permanent Magnet Synchronous Motor In Tendon Skew Rolling Mill

The Permanent Magnet Synchronous Motor(PMSM)has many advantages,such as high efficiency and small size,so it is widely used in industrial production.Direct Torque Control(DTC)is characterized by short response time as well as simple process of calculation.However,the excessive torque ripple limits its application in practice.In order to improve the control performance of PMSM DTC system,based on sliding mode variable structure theory,fractional order theory is introduced in this paper,and main contents are as follows:Firstly,this paper analyzes the mathematical model of PMSM in stationary three-phase coordinate system,stationary two-phase coordinate system,and rotating two-phase coordinate system,and gives a brief overview of the principle of direct torque control of PMSM.In order to overcome the problem caused by excessive torque ripple,space vector modulation(SVM)technology is introduced,and the principle of operation and defects of SVM-DTC system are analyzed.Secondly,aiming at the problem of low control precision caused by PI controller used in speed and torque loop of SVM-DTC system,a fractional order sliding mode controller for torque and flux linkage is designed.The fractional integral term is introduced in the design of sliding mode switching surface,which not only keeps the fast response of DTC system,but also greatly reduces the ripple of torque and flux linkage.In addition,combining with the load disturbance observer,a composite sliding mode speed controller is designed.The simulation results show that with these improvements,the torque ripple is effectively reduced and the precision of control is enhanced.Finally,based on the traditional sliding mode observer,the fractional calculus theory is introduced into the mathematical model of permanent magnet synchronous motor,and a fractional order sliding mode observer is designed,which combines with the phase-locked loop technology,in order to solve problems in the traditional sliding mode observer,such as lag of phase.The simulation results show that the improved observer can estimate the rotorposition and speed with higher accuracy.